This invention is generally directed to developer conditions and toner compositions, and more specifically, the present invention is directed to developer compositions, and toner compositions containing certain charge enhancing additives. In one embodiment, the present invention is directed to developer compositions containing toner particles, and polyanhydride resins as charge enhancing additives, which additives impart a negative charge to the toner resin particles. The polyanhydride materials can also be selected as resin binders for electrostatic toner compositions. Developer compositions containing the charge enhancing additives of the present invention are useful for causing the development of electrostatic latent images, including color images. Furthermore, the toner compositions of the present invention can be selected for use with common carrier particles of the same composition, especially with regard to the development of colored electrostatic images.
Developer compositions containing charge enhancing additives are known in the prior art, particularly, those compositions containing charge enhancing additives which impart a positive charge to the toner resin. However, very few developer compositions are known wherein the charge enhancing additives are selected for the purpose of imparting a negative charge to the toner resin particles. Examples of positively charged systems include those described in U.S. Pat. No. 4,298,672, wherein there is disclosed toner compositions containing alkyl pyridinium halides as charge enhancing additives. More specifically, this patent discloses developer compositions containing from about 0.1 percent by weight to about 10 percent by weight of cetyl pyridinium chloride as a positive charge enhancing additive. Further, there is disclosed in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium compounds as charge control agents for electrostatic toner compositions. A similar teaching is described in U.S. Pat. No. 4,079,014 with the exception that the charge control agent disclosed a diazo compound.
Moreover, there is disclosed in a co-pending application developer compositions containing as negative charge enhancing additives orthohalophenyl carboxylic acids, including for example, 2-fluorobenzoic acid, 2,6-difluorobenzoic acid, 2-fluoro-6-chlorobenzoic acid, and the like.
While the referenced charge enhancing additives are suitable for their intended purposes, there continues to be a need for new charge enhancing additives, particularly those charge enhancing additives which impart a negative charge to the toner resin particles. Additionally, there continues to be a need for charge enhancing additives which can be easily uniformly dispersed in the toner resin particles, and wherein the resulting developer toner composition has a narrow charge distribution, thereby allowing improved image quality. Furthermore, there continues to be a need for a charge enhancing additive which is relatively free from toxicity problems. Additionally, there continues to be a need for charge enhancing additives that are insoluble in water, and insensitive to various humidity conditions, which additives can also be selected for use as the toner resin particles.